Refracting cover-glass for automobile-headlights.



W. CHURCHILL.-

REFRACTINB COVER GLN 3S FUR AUONlUBLE HEADUGHTS.

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se. www Miriam- Specification of Letters Patent.

Appucauon mea october a, i917. serial no. 194,516.

To all whom t may concern.'

Be it known that I, WiiiLiAM CHURCHILL, a citizen of the United States of America, and a resident of Corning, N. Y., have invented certain new and useful Improvements in Refractiiig Cover-Glasses for Automobile- Headlights, ol which the following is a specification.

The automobile headlight now in common use comprises a light source, a reflector and a cover glass, the arrangiiiient of the parts being smh that. the mirror reflects light issuing troni its` local point` iu an approximately parallel beam. lnasmuch as commercial light sources are not point sources, therrl exists a certain amount of dispersion of the beams projected by the projectors. 'lhis is objectionable, in that the rays reflected by thtvl mirror upwardly and forwardly from the principal axis of the niirror are thrown into the eyes of the approaching driver with the eli'eet. of blinding him, so thatlegislation has been enacted., in many of the States requiring that none of the rays from the reflector shall rise ahove a plane parallel with the ground level on which the car is moving. It has been proposed foi' the purpose of avoiding this upward projection of certain reflected rays above the principal axis of the headlight to press on the cover glass a series of prisms so proportioned that they will cause a downward deflection of the rays passing therethrough e ual tothe angle formed between the upwar ly projecting rays falling thereon and the principal axis of the headli ht.

If rays projected by the reflector o a head light from any racticable source be analyzed, it will be ound that each part of the reflector is the source cfreflected rays issuing therefrom in a cone, the angle of which s the same as the angle at such point of the 1i reflector subtended by the corresponding dimansion of the source. Thus the amount of vertical divergence of the rays projected from any p'art of a reflector will vary with the shape of the light source. l the source be spherical, it will be found that the maximum vertical divergence will be from points on the Areflector located at a slight distance from its intersection by the principal axis such points beinglocated in a circle, and the divergence decreasiny at points inside and outside such zone. Iig on the other hand, the source of light be not` in the form of a considerable axial length in respeet'wtgL its breadth, points of maximum verticalsprea'd are created near the top and bottom-ofthe i 1 f i reflector without a corresponding increase of vertical spread on corresponding,` oi'iits Patented Nov. o. 1918i on the horizontal axis of the4 reuectpt. i

Thus points of equal spread'vtith vsuch a light` source are no longer arranged in acircular path, but are arranged in .elliptical paths, the major axes of which are vertical.

n either case, points located in horizvontafl,y

zones across the reflector are not ,Seats ,of equalvertical spread of rays, .mdhence a horizontal prism of uni-formbase angle,` is

formed at one point. to properly correct the divergence of the reflected rays passing therethrough, will not properly correct'ver-` 7'5"] "i tical spread of reflected rays passin through it at other points of its length. his has,

been recognized and attempts have` been made to meet it, either by giving to the prism throughout its lengtlra corrective value equal to the desired corrected value i for the rellected rays of maximum divergence falling thereon at any point (in which case an over-correction is made asto otherA points), or ,else the surface of the prisms have been warped so that each prism `has a hase angle dillerent at different points of its length, in accordance with the desired `corrections to be made at the several oints.

This latter is inconvenient as anianu actur-A ing problem, and it is the purpose of, this invention to so construct refractive prisms that with a fixed angle, they will have a` of horizontal zones, itwill, therefore, be rnoted that the point of maximum vertical I'divergence of each zone is at or near the centerthereot, with points of minimum vertical divergence at the outer ends.

I ropose to take advantage of this fact to i viate the ynecessity of warping the risms by forming one of the refracting aces of each prism on the surface of the frustum of a cone, whose axis is so situated in lexpect to the optical axis of theheadlight tha the prism formed thereby passes through points on different horizontal zones of the cover glass. As the downward dc- Hection produced by each point of such a rism varies with the cosine of the angle ormed between the radius to such point and the vertical, each prism, while havintr a uniform base an rle throughout, varies through ii in power of vertical refraction. By a proper selection of constants such prisms ma be caused to pass through such points on t e cover lass that the verti cal refractive power of tie prism at several points on the cover glass will be such as to cause the amount of vertical correction de sired forl such points.

My invention, therefore, consists in a cover lass having such prisms thereon, and it urtlier consists in a cover glass having in addition to such prisms ancillary refraeting elements adapted to correct verti lal divergence at. certain portions of the cover glass'. and to causo side-dispersion, as will he here inafter more fully described.

Referring to the accompanying drawings in which corrcspondin parts are designated by corresponding mar is of reference:-

Figures 1 and 2 are diagrams illustrative of principles made use of in this invention.

Figs. 3 and l are an elevation and section.Y respectively, through a cover glass illustratiie of niy invention.

Figs'. and t5 are a rear view and section. respectively, illustrating a cover glass eiuhodying,r the preferred forni of in v invention.

Considering a curved prism. one of whose faces is foi-ined on the curved lsurface ol' the frustuin of a conc and another of whose faces is formed by the Hat base of the cone, let the face a-b, Figs. 1 and 2, be a curved face and the face a-c, the flat, face. respectively.` the axis of the cone hy which they are formed being d-f. Then all ralvs, such :olf/tmf, parallel `iiith the axis f-('` fall on"-\ the face (1.-c at a normal thereto and enten@ ma Mmmm' (Hmmm.

the rpi-isni without refraction. They h nvt; evei, sutfer refraction on passinghiut ofhie prism throiurh the face a-l; and are lient in the direction tl'-c across the axis, the angle f/-c-f. measuring the refraction of the rays, being dependent on the angle r' uw() and the index of the refraction of the prisms. As this angle is uniform at all portions oi' the prism, all rays parallel with the. axis 1 -d will bc bent toward such axis equally. Considering the axis d-fl as horizontal, the ray e--f striking the prism vertically above such axis is deflected downwardly in thel vertical plane toward the axis d-d through the same degree that a ray parallel to d-d' striking t e prism at the 1,esa,dvi

point; e"horizontally to one side of the axis d-d' is deflected sidewise in the horizontal plane of the axis. Rays parallel to the axis d (l and striking the rism at )oints between the oiiits e and e', efore referred to, will be tirected toward the axis cI-fl downwardly and sidewise. in a plane inclined to the vertical and in which the point e and the axis cl-r are located. The vertical component of this deflection will have as a factor the cosine of the solid angle bctween the planes La-fl and c--dc/, that is to say, the cosine of the angle qd-1" (Fig. 2) between the vertical and the radius to the circle formed hy the prism at .the point ei'. Thus a circular prism of uniform angle possesses for rays' axial to the cone of which it forms a part of the hase vertical refractive power at ditl'crent points around its circle. 1n a like manner the horizontal refractive power of such a prism varieswith the sine of thc angle i'fff-wfg.

lI propose to [alte advantage of these properlles` of such a prism to obtain the desired aniount of vertical dispersion at ditfercut points on the cover glass. by causing a prisui of selected corrective value at its upper portion to pass through such other points on the cover glass that the vertical corrective power of such points of the prism will he such as t'o cause the vertical correction for reticcted rays desired at such points. [nasniuch as with a focused light source of diniensionsl actually in use every part of a cover glass demands refractive vertical correction to sonic. extent, it is iuiprzu-ticahle to use the lower half of the solid conical frustuni for which the upper part is used, for such lower half will produce upward refraction if the axis ot' the cone be parallel with the principal axis' ol' the headlight, or to use any hut a part of thi` upper half of the irustuni. as the portions` thereof located at the ends ot' the horizontal radii possess, as 110 ahove pointed oitt, no downward refraction. lior this reasoul 4prefer to use only the. portions ot' the frits-tuin located at an appreci above the axis thereof, so t iat all portions of each prism will have 116 a ve tical eonuoncnt. of refraction. i

het'erringir to ["ig. I. let it be presumed that the cover glass l shown therein should, for the purposes had in view and when used t iu connection with a lgiven reflector and a 120 focused lig-ht lsource` provide for downwardly hendingrays passing therethrough nt the several points noted thereon of the degreesl indicated at such points. which amounts will he hereinafter called the dcsired correction. [t will he noted that this figure gives values. for purposes of illustration` of two points vertically over the center of the cover glass, this latter being the point at; which the principal axis of the fheadlight asses therethrough. One 0f these points (mi) calls for 4 degrees of correction, and I accordingly place on the cover glass at such point a curved prism 2 the angle between the front and rear face of which measured on its radius will provide for the correction of the amount called for. The point n. located to one side of the vertical medial line and at a lower level than the point m has a desired correction less than that of the oint m, namely, a correction of 3 degrees. o obtain this correction by the same prism (2*) that provides for the correction at the point m, such prism is 'formed by a part of a frustum of a cone. the base radius of which is so selected that the curved prism formed thereby will cover the point n. and the axis of which, While parallel with the principal axis of the headlight, will be so situated that it will pass through the cover glass at the point 0 so selected that the angle 'mf-o-Jnl made by the radii from such axis to the points m and n is of such value that the cosine of the angle 'mf-own multiplied by the corrective value of the prism at m will be substantially equal to the correction desired at n.

inasmuch as, generally speaking, the point of smaller desired corrective value (n) will be nearer the horizontal diameter ot the cover glass than the point of larger wr rective value of the same prism, this means that the axis of the frustum will be dccentered from the center h of the glass and the principal axis of the headlight, and will be below and parallel thereto. The point p is also on the vertical diameter and requires a. greater correction than m., and therefore I place on the cover Iglass at such point a second prism 2C giving at the point p the dcsired correction. This prism, in view ot' the greater correction required at point p will be formed by a frustuin whose hase angle is greater than that forming the face of the prism 2", and the principal axis thereof will be so located that it will, under the rule, provide, as above stated. the desired correction at the point q. (,ibviously the axes of the two frusta may or may not coincide. ln the first the prisms will bc fyoir centric, which is convenient in manufacture, and to accomplish this a latitude in ratio of the correction obtained lo the, cor rection required, may be allowed. ln Fig. 3 I have shown the axes ot' the two frusta non-coincident, the axis oi' the frnstum forming prism '22" intersecting the plate at the point o.

Obviously the several partial frusta may be superimposed the one upon the other, as is illustrated in Fig. 4. This results in an objectionable thickness ot' the cover glass, and hence I prefer to form the prisms into a series of steps, that is, to foi In cach prism by a part of that portieri of the frustum which remains after removing therefrom a cylinder ot the same height whose diameter is the same as the smaller diameter of the frustuni.

The application of these principles to a cover glass is shown in Figs. 5 and il. Here the cover glass has formed on one face thereof a series of concentric prisms 2, 2b, etc., such prisms being of thc charr acter before described and being curved around a common axis o located below and some distance from the renter le, of the glass` each prism being of uniform angle throughout its length. but the several prisms varying between themselves in angle, in accordance with the principles already stated. The distance frm-o is such that the several prisms strike the annular shoulder il formed near the edge of the glass above the lcvcl of the axis 0 so `that all portions of each prism have a downward component of refraction, while certain portions of the several prisms have also a side-cennponcnt of refraction. which is desirable in providing for the horizontal spread of thc beam.

The prisms are by prctercnre formed only on the rear and inncr faces of the cover Aglass, in order to leave :i smooth face to pre vent the lodgmcnt of dirt. Obviously my invention is not restricted in this respect.

It may under certain circumstances be desirable to place on the cover glass retractng elements other than the circular prisms, in order to provide l'or greater side spread than is given by such prisms, or for other reasons. Such elements :irc shown in Fig. in which as the common center of curvature o is located at a distance below the principal axis of thc headlight less than the radius of the face `of the cover glass, a lune is formed between thc ring Il and the inner prism 2g at the bottom pari of the cover glass on which there are no circular prisms. This space may be formed in any desired means with a view ot preventing lare or of obtaining side spread, and for tiis purpose l may use, as shown in the drawings, nogal-ae -l such, for instance, as shown in the application ot' (laire and Pascucci, liled in the United Stairs lalcnt (lllice on the lith day of December. llll, `serially numllcrcll 136,437.

ina-enrich as there is a tendency of the prisms to suck up in the molds, especially near the ends thereof. l prefer to place on such prisms strcngfthoningr ribs 5 extending radiadv thereof and acting, duc to the fact that they quickly chill. lo prevent distortion in raising the plunger.

llaving thus described my invention, what l claim and desire to secure b v Letters Patent is :---v

l. A rcfracting cover glass for automobile headlights, having thereon a series of prisms, one of the refracting faces of each prism being; on the surface of a conical frnstnm whose axis is so plaeetl and whose lame is sneh that the l eve1'al prisms at elif ferent points throughout their length have verti al refractive power HnlmtantialhY equal to the vertical refractive power necessary at ,such points nt' the eover glass to overcome the upward lirergenee of rays from the lentllight reflector falling on the rover glans at such points.

2. A reflui-tintr eorer glass for automohile headlights, having,t thereon a laerien of prisms, one of the refraetingr tart.` of each prism being on the surface of a eonieal frustum whose axi interseeth` the plane of the glass away from the center thereof at such a distanee that the several prisms at tlierent points throughout their lengthn have vertical refractive power substantially equal to the veltieal refrartive power neeessary at Snell points of the eover glass to overcome the upward divergence ot' rays from the headlight refieetor falling on the cover glass at such pointS.

il. A refracting: cover ,fg-las` for automohile headlights. haring thereon a laerien` of prisms. one of the refraeting;r fares of eaeh prism heinglr on the sin-fare of a eonieal frnstum whose axis is parallel with they axis; of the headlight and is at auch a (listanee therefrom that the vseveral primis at tlitferent points throughout their length have vertieal refractive power substantially equal to the vel-tival refractive power necesaary at yurli poin` ot' the eorer einen to orereome the upwarcl ilirergenee, of ray` from the heailligln rein-eter falling nn they eover glass at Hut-h point,

i. eurer for aute'nnohile heaillightbhav in;,r thereon allure the optieal axis a aerien` ol' eurreil ref'rarting prisme, nml below the optical axi a aeries, ot' horizontal prisms, the renter nl' lhe ellrvailire olI the elilvetl prinnia heilig helow tht` optie-.l axis of the headlight,

3. A rover l'or automobile heaillighta having r thereon a .aerien of eurveel refraeting prisms. eaf'h priani heing formell h3* not more than the upper half of a conical frnatnni whose axi is located below the optiea! a\i.-` of the headlight, andralso having a eerie@ of downwardly clefleetinffprismey ioeatefl hetween the ends of the inner of sneh eurveil prisms.

(L A retraining rover glass for :intornohile lleatlligfhta,y having thereon a series of prisma, certain oi' the prisms haring thin transverse flanges projectingr therefrom and serving hy their quick cooling to prevent sut-king up of auch prisms in molding.

In testimony whereof I have .signed my name this 27th day of September, 1917.

WILLIAM CHURCHILL. 

